Method for pre-preg manufacturing

ABSTRACT

A method of making a composite part comprises covering a mold tool for a composite part with a parting film, the parting film comprising a polymer sheet and a pressure sensitive adhesive. The parting film is positioned so that the polymer sheet is between the mold tool and the pressure sensitive adhesive. At least one layer of pre-preg is layed up on the parting film covering the mold tool to form a layed-up composite part. The pre-preg comprises an adhesive. The layed-up composite part is removed from the parting film.

DETAILED DESCRIPTION Field of the Disclosure

The present disclosure is directed to a pre-preg molding process formanufacturing composite parts.

BACKGROUND

Pre-preg is a term for “pre-impregnated” composite fibers in which amatrix material, such as epoxy, is already present in the fiberreinforcement before molding occurs. Pre-preg manufacturing techniquesare often employed to manufacture composite parts for a variety ofcommercial uses, including the manufacture of aircraft, for example.Composite part manufacturing using pre-preg manufacturing methods can bea rate limiting step in the production of composite products.

Pre-preg is currently laid up on a molds covered with a polymer partingfilm during the manufacture of composite parts. In conventionalpractice, the parting film is replaced after every part is made, whichconsumes manufacturing time between parts and creates material waste inthe form of the disposed of parting films. Furthermore, in order toenable easy release of pre-preg, the parting films are composed ofnon-adhesive polymer sheets, so that the adhesion between the pre-pregand parting film is low. Due to the low adhesion, the pre-preg may sliparound on the surface during placement, thereby consuming additionaltime.

Thus, there is a need in the art for improved parting films andtechniques that can provide improved efficiency in pre-pregmanufacturing processes.

SUMMARY

The present disclosure is directed to a method of making a compositepart. The method comprises covering a mold tool for a composite partwith a parting film, the parting film comprising a polymer sheet and apressure sensitive adhesive. The parting film is positioned so that thepolymer sheet is between the mold tool and the pressure sensitiveadhesive. At least one layer of pre-preg is layed up on the parting filmcovering the mold tool to form a layed-up composite part. The pre-pregcomprises an adhesive. The layed-up composite part is removed from theparting film.

The present disclosure is also directed to a method of preparing a moldtool for lay up of a pre-preg. The method comprises covering a surfaceof the mold tool with a parting film, the parting film comprising apolymer sheet and a pressure sensitive adhesive. The parting film ispositioned so that the polymer sheet is between the mold tool and thepressure sensitive adhesive. The pressure sensitive adhesive is capableof adhering to at least one layer of pre-preg during a laying up processfor manufacturing a composite part, and of releasing the pre-preg afterthe laying up process is complete.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the present teachings, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrates aspects of the present teachingsand together with the description, serve to explain the principles ofthe present teachings.

FIG. 1A shows a method for manufacturing a composite part using apre-preg manufacturing technique, according to the present disclosure.

FIG. 1B shows the continued method of FIG. 1A for manufacturing acomposite part using a pre-preg manufacturing technique, according tothe present disclosure.

FIG. 1C shows the continued method of FIGS. 1A and 16 for manufacturinga composite part using a pre-preg manufacturing technique, according tothe present disclosure.

FIG. 2 shows a FTIR spectra of a SOLPRENE® 9618 pressure sensitiveadhesive (“PSA”) coated parting film and residue after removal of thesample from the ATR crystal, according to an example of the presentdisclosure. All residue peaks are less than 1% the intensity of the PSAcoated parting film peaks.

FIG. 3 shows a FTIR spectra of a CALPRENE® 540 adhesive coated partingfilm and residue after removal of the sample from the ATR crystal,according to an example of the present disclosure. All residue peaks areless than 1% the intensity of the PSA coated parting film peaks.

FIG. 4 shows a schematic drawing of a tack testing process, according toan example of the present disclosure. The parting film is on the bottomof the probe with the tunable adhesion surface facing the pre-preg.

FIG. 5 shows FTIR analysis of resin transfer to CALPRENE 540 adhesive,according to an example of the present disclosure. The intensity at 3365cm⁻¹ gives a surface concentration of <1.1 μg-resin/cm² after 15pre-preg contact cycles.

FIG. 6 is a graph of FTIR analysis of resin transfer to SOLPRENE 9618pressure sensitive adhesive, which shows a surface concentration of <1.0μg-resin/cm² after 15 pre-preg contact cycles, according to an exampleof the present disclosure.

FIG. 7 shows FTIR spectra of CALPRENE 540 pressure sensitive adhesiveand pre-preg resin, according to an example of the present disclosure.Insets show detail around three regions where bands from the resin inthe pre-preg do not overlap with bands from the adhesive; (left inset)around 3365 cm⁻¹ and (right inset) around 1510 cm⁻¹ and 1145 cm⁻¹.

FIG. 8 shows an expanded view of the background region for spectra inFIG. 7. The offset of the baselines can be seen. The approximatelocations for a two-point linear background correction are indicated.

FIG. 9 shows a spectrum and background in transmission for pressuresensitive adhesive with epoxy resin from the pre-preg on the surface,according to an example of the present disclosure. Bands from the resinand adhesive are indicated. The background (straight black line) wasobtained from the two points shown by the dots at wavelengths of 3800and 2200.

FIG. 10 shows background corrected, zero baseline, absorption spectra ofpre-preg resin on pressure sensitive adhesive, the adhesive withoutresin and adhesive with varying amounts of resin, according to anexample of the present disclosure. The inset shows the peak intensityfor the C—H stretch of the adhesive.

FIG. 11 shows a calibration curve from standard samples of epoxy resinfrom pre-preg on pressure sensitive adhesive, according to an example ofthe present disclosure. The top axis gives resin solution concentrationsfrom stock solution dilutions of 1:10, 1:20, 1:50, 1:100, 1:200, 1:300,and 1:500. Bottom axis gives resin surface concentration from 10 μldrops spread over 0.44 cm². The circles show data points from 32 scanspectra. Open squares show data from 1024 scan spectra, used for low, <1μg/cm², concentrations and to determine the detection limit as describedbelow (FIG. 13). Linear fit of the 32 scan spectra is shown fordilutions of 1:10, 1:20, 1:50, and 1:100.

FIG. 12 shows a calibration curve for resin transfer to adhesive for anHRL FTIR system, according to an example of the present disclosure.Resin surface concentration from IR intensity at 3365 cm-1; best fit(solid line), ±1σ upper and lower limits (dashed lines).

FIG. 13 shows a low concentration of pre-preg resin on CALPRENE 540adhesive, according to an example of the present disclosure. Spectra areshown for standard samples from dilutions of 1:200 (dotted lines, 2spectra) and 1:500 (dashed line). After background correction,intensities for the adhesive (2800 cm⁻¹ to 3100 cm⁻¹) overlay to within<5%. Inset shows region for resin absorption on an approximately 50×expanded scale.

It should be noted that some details of the figures have been simplifiedand are drawn to facilitate understanding rather than to maintain strictstructural accuracy, detail, and scale.

DESCRIPTION

Reference will now be made in detail to the present teachings, examplesof which are illustrated in the accompanying drawings. In the drawings,like reference numerals have been used throughout to designate identicalelements. In the following description, reference is made to theaccompanying drawings that form a part thereof, and in which is shown byway of illustration specific examples of practicing the presentteachings. The following description is, therefore, merely exemplary.

The present disclosure is directed to a method for manufacturing acomposite part using pre-preg manufacturing techniques. Referring toFIGS. 1A to 1C, the method involves covering a surface of a mold tool102 with a parting film 104 comprising a polymer sheet 106 and apressure sensitive adhesive 108. The pressure sensitive adhesive 108 canbe in any suitable form that will provide the desired adhesion betweenthe parting film 104 and the pre-preg, such as a layer deposited orotherwise attached to the polymer sheet 106. Referring to FIG. 1B, atleast one layer of pre-preg 110 is layed up on the parting film 104 toform a layed up composite part 112. The pressure sensitive adhesive 108allows the at least one layer of pre-preg 110 to adhere to the partingfilm 104 during the process, while having the ability to be removed fromthe pre-preg without leaving detrimental amounts of residue or otherwisedamaging the composite part that is formed from the pre-preg.

As shown in FIG. 1C, after the lay up process is complete, the moldedcomposite part 112 is removed from the parting film 104. During removalof the composite 112, the adhesive force holding the composite part 112to the pressure sensitive adhesive is overcome by applying a force thatis greater than the adhesive force to pull the composite part 112 fromthe pressure sensitive adhesive. The laying up step of FIG. 1B and theremoving step of FIG. 1C can be carried out any number of times, such asone or a plurality of times, to form a desired number of composite parts112 without removing the parting film 104 from the mold tool 102. As anexample, the laying up step and the removing step can be carried out 5to 50 times, such as 10 to 30 times or 15 to 25 times.

The pre-preg 110 can be any suitable pre-preg. Pre-pregs are well knownin the art and generally comprise fibers in an adhesive resin. As anexample, the pre-preg can comprise a carbon fiber reinforced plasticand/or one or more epoxy chemical groups that effectively act as anadhesive for adhering multiple pre-pregs together. The epoxy of thepre-preg also potentially adheres to other materials, such as thepressure sensitive polymer adhesive 108 of the parting film. As anexample, the epoxy based pre-preg employed in the processes of thepresent disclosure can be said to have a threshold adhesive strengthagainst a steel plate of greater than 10 kPa, such as about 30 to about120 kPa, where the adhesive strength is measured using the tack test asdescribed below with respect to FIG. 4, except that the steel probe isused without attaching a parting film 104.

The polymer sheet 106 can comprise any non-adhesive polymer materialthat is non-adhesive to the pre-preg 110 and that has the structuralability to act as a standalone substrate, conform to the mold surfaceand withstand other pre-preg processing conditions. The polymer sheet106 generally does not contain acrylics, rubber,styrene-butadiene-styrene copolymers or other styrene copolymers. Forexample, suitable non-adhesive polymer sheets can comprise a materialchosen from the polymers of polyethylene, polyethylene terephthalate(“PET”), fluorinated ethylene propylene (“FEP”), nylon and combinationsthereof. The thickness of the polymer sheet 106 can range, for example,from 0.0001 to 0.01 inches, such as 0.001 to 0.004 inches.

The term “pressure sensitive adhesive” is defined herein to designate adistinct category of adhesive material that in a dry form (e.g.,substantially free of both solvent and water) are aggressively andpermanently tacky at room temperature and that firmly adhere to avariety of dissimilar surfaces at room temperature, including paper,plastic, glass, wood, cement and metal, upon mere contact without theneed of more than 20 pounds per square inch of pressure being applied.These products require no activation by water, solvent or heat in orderto exert a strong adhesive holding force toward such materials. Theyhave sufficient cohesive holding power and an elastic nature so thatdespite their aggressive tackiness, they can be handled with the fingersand removed from smooth surfaces without leaving a significant residue.The phrase “substantially free” is defined herein to mean 5% by weightor less relative to the total weight of the composition. In an example,the “pressure sensitive adhesive” can have 0 to 5% combined weight ofboth solvent and water, such as 0 to about 3% by weight based on thetotal weight of the composition.

The pressure sensitive adhesive has the ability to conform to thesurface of the pre-preg under pressure, thereby increasing surface areacontact and, in turn, the Van der Waal forces between the adhesive andthe pre-preg. It is believed that the increased Van der Waals forcesprovide the primary mechanism for adhesion. Because the adhesive can beapplied in a dry form, drying or curing of the adhesive is not necessaryto accomplish the desired adhesive force. Significant adhesion is notaccomplished by chemical bonding, such as covalent or ionic chemicalbonding, between the surfaces, as would occur with a dried or curedadhesive.

The pressure sensitive adhesive 108 is chosen to have the property ofadhering to the pre-preg 110 sufficiently so as to significantly reduceslipping during lay up while, at the same time, having the ability torelease the composite part 112 after lay-up is completed, withoutdamaging the composite part (e.g., without pulling out carbon fiber ortransferring material to pre-preg that will change the cured partproperties in an undesirable manner). As an example, the pressuresensitive adhesive can have a peak tensile strength (kPa) between thepre-preg 110 and the adhesive coated parting film 104 of about 1 kPa toabout 500 kPa peak adhesion force, such as about 3 kPa to about 50 kPapeak adhesion force, or about 5 kPa to about 25 kPa peak adhesion force,where the peak adhesion force is determined as describe herein withrespect to FIG. 4.

The thickness of the pressure sensitive adhesive 108 can range, forexample, from 0.0001 to 0.01 inches, such as 0.001 to 0.004 inches, or0.001 to 0.002 inches. The pressure sensitive adhesive 108 of theparting film 104 can be reusable over multiple lay-up cycles to save thelabor and waste of using a new parting film for every part. In addition,the pressure sensitive adhesive can have a glass transition temperaturebelow 20° C., such as about negative 150° C. to about 0° C. or aboutnegative 100° C. to about negative 50° C.; and can have greater than a50% elasticity at room temperature (e.g., sufficient elasticity at 20°C. so as to be capable of exhibiting greater than 50% extension), suchas about 100% to about 1000% elasticity. It is believed that the highelasticity can allow the material to hold together during release,thereby reducing the amount of adhesive residue that remains on thecomposite part.

The pressure sensitive adhesive can comprise linear or branched, randomor block polymers having one, two, three or more monomer units. Examplepressure sensitive adhesives can comprise a material chosen from theadhesives of acrylic resin, polyurethane, rubber,styrene-butadiene-styrene copolymers, ethylene vinyl acetate, styreneblock copolymers, and combinations thereof, such asStyrene-ethylene/butylene-styrene (SEBS) block copolymer,Styrene-ethylene/propylene (SEP) block copolymer,Styrene-isoprene-styrene (SIS) block copolymer, or combinations thereof.As an example, the pressure sensitive adhesive comprises a materialchosen from the adhesives of styrene-butadiene-styrene block copolymers,styrene-butadiene-styrene random copolymers and combinations thereof.

The pressure sensitive adhesive can include a block copolymer having afirst block and a second block, the first block having a glasstransition temperature of less than 20° C. and the second block having aglass transition temperature of greater than 20° C. Styrene-butadienecopolymers are one such example, where butadiene is a monomer that formsa polymer with a glass transition below room temperature whilepolystyrene has a glass transition temperature of 90-100° C. Specificexamples of such polymers are shown in Table 2 below.

The polymer of the pressure sensitive adhesive can have a relativelyhigh molecular weight to reduce or eliminate residue from the pressuresensitive adhesive transferring to the pre-preg during processing. As anexample, the mass average molecular weight can be about 70,000 g/mol toabout 1,500,000 g/mol, such as about 80,000 g/mol to about 1,200,000g/mol, or about 100,000 g/mol to about 1,000,000 g/mol.

The amount of block copolymer in the pressure sensitive adhesive can beany suitable amount that will provide the desired properties. As anexample, the amount of block copolymer can range from 50% to 100% byweight of the pressure sensitive adhesive, such as 80% to 99%, or 90% to96% by weight, based on the total weight of the pressure sensitiveadhesive. Because the adhesive is not dried or cured, the range ofcopolymer can be approximately the same both before and during adhesionof the pressure sensitive adhesive to the pre-preg, as well as afterrelease of the composite part from the adhesive.

The compositions of the present disclosure can be additive free, meaningthat only block copolymer is employed as the adhesive. Alternatively, inaddition to the block copolymers describe herein, the pressure sensitiveadhesives of the present disclosure can optionally include any othersuitable ingredients in any desired amounts, such as carrier liquids,plasticizers, tackifiers, oxidation stabilizers and UV stabilizers andother such components to manage viscosity, adhesion strength, theability to retain moisture content over time and other desiredproperties. Ingredients not expressly recited in the present disclosurecan be limited and/or excluded from the pressure sensitive adhesivedisclosed herein. Thus, the amounts of the thermoplastic polymer and anyoptional ingredients, such as carrier liquid, plasticizer, tackifiers,oxidation stabilizers and/or UV stabilizers can add up to 90% to 100% byweight of the total ingredients employed in the composites of thepresent disclosure, such as 95% to 100% by weight, or 98% to 100% byweight, or 99% to 100% by weight, or 100% by weight of the totalingredients.

As mentioned above, release of the composite part from the pressuresensitive adhesive is accomplished by applying sufficient tensile forceto overcome the Van der Waals attraction between the composite part andthe pressure sensitive adhesive. When applying force to release thecomposite part, the pressure sensitive adhesive will stretch as it pullsaway from, thereby progressively reducing the shared surface area withthe composite part, while still holding together so as to fail at theinterface between the composite part and the adhesive. The elasticityallows the composite part to be more easily removed and helps to limitthe amount of residue that remains on the composite part.

Referring again to FIG. 1C, removal of the layed-up composite part 112can be performed in any suitable manner. For example, removal can beperformed with a tool that adheres to the composite part 112 morestrongly than does the pressure sensitive adhesive 108 of the partingfilm. For example, the tool can be a vacuum chuck. As another example,the tool can have a surface comprising an adhesive that adheres withsufficient strength to the composite part 112 so as to be able toseparate it from the parting film 104.

After removal of the composite part form the mold, little or no pressuresensitive adhesive remains on the composite layer. As an example, lessthan 10 micrograms/cm² of the pressure sensitive adhesive remains on asurface 114 of the completed part that was in contact with the pressuresensitive adhesive 108 during laying up of the pre-preg 110. As anotherexample, less than 5 micrograms/cm², such as less than 2 micrograms/cm²or less than 1.5 micrograms/cm², of the pressure sensitive adhesive 108remains on the surface 114 of the completed part. The amount of residuecan be determined using the residue analysis procedure as described inExample 3 below.

The parting film 104 can be made by any suitable method. For example,the pressure sensitive adhesive can be applied onto a polymer sheet 106using coating techniques for polymer deposition. A variety of polymercoating techniques are known in the art. If desired, the polymer sheetcan be plasma-treated to improve adhesion between the non-adhesivepolymer material and the pressure sensitive adhesive 108. Any suitableplasma treatment techniques for improving adhesion can be used.Techniques for plasma treating polymer films and other substrates aregenerally well known in the art. Corona treatment, for example, is acommon industrial plasma treatment procedure that occurs in film coatingproduction lines.

EXAMPLES Example 1—Sample Preparation and Adhesion Properties

Pressure sensitive adhesives were applied on non-adhesive parting filmsubstrates using the following process. The adhesives and the partingfilm substrates are listed in Table 1 below. Parting film substrateswere first Corona treated or plasma treated to improve adhesion betweenthe pressure sensitive adhesives and the parting film substrate toprevent delamination during removal of pre-preg. Adhesives were coatedonto the Corona treated parting film substrates as solutions in tolueneat a loading of 37 g/m² (one sample was made at 25 g/m²).

Example 2—Sample Preparation and Adhesion Properties

Adhesion (e.g., tack) measurements for the prepared samples were made asfollows: Mode 1 tack was measured using a Malvern Kinexus rheometer witha 0-50 N load cell. Pre-preg samples one day out of the freezer werepreconditioned at 55% relative humidity (“RH”) and 72° F. for 4 h. Thepre-preg used for testing in the present disclosure was a Toray3900-2/T800S type pre-preg comprising an intermediate modulus (“IM”)carbon fiber and epoxy resin. A parting film including pressuresensitive adhesive was attached to a flat, 8 mm diameter round steelprobe and pre-preg was adhered to the rheometer bottom plate. The tacktest was performed by bringing the probe down onto the sample, applyingpressure equivalent to 12″ of mercury on the sample with the probe for30 seconds, and pulling up the probe at 1 mm/s (FIG. 4). As shown inTable 1, the tested pressure sensitive adhesives show a wide range ofadhesion levels to pre-preg.

TABLE 1 Pressure sensitive adhesives on parting films Peak tensileAdhesion strength (kPa) energy (μJ/cm2) between pre- between pre- pregand preg and Adhesive Adhesive Parting film adhesive coated adhesivecoated candidate chemistry substrate parting film parting film DynasolSOLPRENE Poly(styrene- Plasma treated 21.4 0.34 1205 butadiene- FEPstyrene) rubber Dynasol SOLPRENE Poly(styrene- PET 12.4 0.17 1205butadiene- styrene) rubber Elvax 4310 Ethylene vinyl PET 101.7 2.99acetate Kuraray Septone Hygrogenated Plasma treated 31.9 0.61 2063styrenic block FEP copolymer Kuraray Septone Hygrogenated PET 49.2 0.872063 styrenic block copolymer Lubrizol HP 4080-20 Polyurethane Plasmatreated 105.6 3.56 FEP Lubrizol HP 4080-20 Polyurethane PET 56.8 1.35Ashland Aroset 1450 Acrylic pressure FEP 95.0 4.30 sensitive adhesiveAshland Aroset 1450 Acrylic pressure PET PSA transferred N/A sensitiveto pre-preg adhesive Avery Dennison Hot melt adhesive FEP & PET PSAtransferred N/A H210 to pre-preg Cattie 8333 Hot melt adhesive FEP & PETPSA transferred N/A to pre-preg Kuraray Kurarity LA Block polymer of FEP& PET PSA transferred N/A 2140 ethyl methacrylate to pre-preg and butylacrylate Nipol DM 1201 Terpolymer of PET PSA transferred N/Aacrylonitrile, to pre-preg butadiene and isoprene

SOLPRENE® 1205, a Poly(styrene-butadiene-styrene) rubber, on PET andplasma treated FEP were selected for further testing because they hadthe lowest adhesion. It was shown using infrared spectroscopy thismaterial was transferring to pre-preg after contact. SOLPRENE 1205 hasan average molecular weight of 52,000 g/mol. Thus higher molecularweight styrene-butadiene-styrene polymer adhesives were tested as shownin Table 2.

TABLE 2 Higher molecular weight adhesives tested Peak tensile strength(kPa) between pre-preg Adhesive Adhesive chemistry and adhesive coatedcandidate and molecular weight parting film SOLPRENE 4302 on 33% styrene68 corona treated WL3800 67% butadiene PET Block polymer Mw = 110k g/molCALPRENE 500 on 30% styrene 49 corona treated WL3800 70% butadiene PETRandom polymer Mw = 110k g/mol SOLPRENE 9618 on 31% styrene 43 coronatreated WL3800 69% butadiene PET (37 g/m² adhesive) Block polymer Mw =800k g/mol SOLPRENE 9618 on 31% styrene 42 corona treated WL3800 69%butadiene PET (25 g/m² Block polymer adhesive) Mw = 800k g/mol CALPRENE540 on 40% styrene 21 corona treated WL3800 60% butadiene PET Multi armrandom polymer Mw = 110k g/mol

The main conclusions from Table 2 are as follows:

-   -   CALPRENE® 540 and SOLPRENE® 9618 were the most attractive        samples.        -   CALPRENE 540 has a desirable 21 kPa peak adhesion force            tack.        -   SOLPRENE 9618 has the second lowest peak adhesion force.    -   Using higher molecular weight adhesives reduced the residue. No        or substantially no material was transferred to pre-preg when        the molecular weight was >100000 g/mol.    -   Transitioning from a block polymer structure to a random        co-polymer at constant molecular weight also decreased adhesion        (SOLPRENE 4302 vs CALPRENE 500).

Except for SOLPRENE 9618, all of the PSAs of Table 2 are formed fromlinear polymers. SOLPRENE 9618 has branch points where additionalpolymer chains grow off the main chain, thus it is a “multi-arm” typebranched polymer. Further, SOLPRENE 9618 is a random polymer that ishighly extensible and has a glass transition temperature below roomtemperature (e.g., has a glass transition temperature of −89° C. andwill undergo 850% elongation without breaking). Both CALPRENE andSOLPRENE are commercially available from Dynasol LLC of Houston, Tex.

Example 3—Residue Analysis

Residue analysis was performed to investigate the propensity formaterial transfer from a pressure sensitive adhesive coated parting filmto pre-preg during lay-up. The procedure for this test consisted ofpressing a material, in this case one of the PSA coated parting films ofTable 2, against an FTIR ATR crystal, collecting a 128 scan absorbancespectrum of the material, removing the material, and collecting a 128scan absorbance spectrum of the residue on the ATR crystal. The residueof SOLPRENE 9618 is shown in FIG. 2 and CALPRENE 540 is shown in FIG. 3.In both cases the residue peak intensity is <1% of the adhesive peakintensity, which is an insignificant residue level.

Example 4—Reusability Data

In order to test reusability for up to 15 lay-up cycles, a method wasdeveloped to quantify resin transfer from pre-preg to the pressuresensitive adhesive coated parting film. Resin transfer increasesadhesion between parting films and pre-preg, which can result in fiberpull out from the pre-preg if a parting film is reused multiple times.Resin transfer was tested by applying a set pressure between a pressuresensitive adhesive coated parting film and pre-preg, as is discussed ingreater detail below. Multiple cycles of resin transfer were performedbetween pre-preg and CALPRENE 540 and SOLPRENE 9618 followed by a tacktest and measuring the resin level on the pressure sensitive adhesivetreated parting film, as is also discussed in greater detail below. Itshould be noted that the tack test was an additional pre-preg contactcycle, thus a sample that has 16 cycles in Table 3 underwent 15 pre-pregcontact cycles. Likewise, a sample that has 2 cycles in Table 3underwent 1 pre-preg contact cycle before the tack test while a samplethat underwent one pre-preg contact cycle only experienced a tack testfollowed by measuring the resin level on the film.

TABLE 3 Resin surface concentration and tack after pre-preg contactcycles Peak adhesion Adhesive energy Sample (# of Resin strength betweenbetween coated pre-preg contact concentration coated parting partingfilm cycles including on surface film and pre-preg and pre-preg the tacktest) (μg/cm²) (kPa) (μJ/cm²) CALPRENE 540 <1.0 21 0.3 (1) CALPRENE 540<1.2 14 0.8 (2) CALPRENE 540 <1.2 26 0.6 (16) CALPRENE 540 <1.0 15 0.4(2) duplicate CALPRENE 540 <1.0 7 0.1 (16) duplicate SOLPRENE 9618 <1.242 0.8 (1) SOLPRENE 9618 <1.0 10 0.3 (2) SOLPRENE 9618 <1.6 17 1.0 (16)

In Table 3, the peak adhesion strength is maintained at <30 kPa formultiple pre-preg contact cycles for all samples. Thus extra resin onthe film does not increase adhesion as is observed with bare partingfilms (non-adhesive polymer substrates without the PSA coating). Basedon these results, PSA coated parting films are reusable.

To simulate multiple pre-preg lay-ups on the same surface andinvestigate the extent of resin transfer from pre-preg to the pressuresensitive adhesive coated parting film reported in Table 3 above,pre-preg contact cycles were conducted with test coupons of CALPRENE 540and SOLPRENE 9618 (the two best performing pressure sensitiveadhesives). For each cycle, a 25 mm diameter disk of adhesive coatedparting film was laid adhesive-up on an optical glass flat. An ˜30 mm×30mm square piece of pre-preg was laid over the adhesive. The piece ofpre-preg still contained the backing sheet, which was facing up. Next asecond optical glass flat was laid on the pre-preg completing the stack.To simulate the contact, a 2 kg weight was placed on the stack for 1minute. This mass is equivalent to ˜300 mm Hg. For multiple cycles, theweight was removed and the pre-preg peeled off the adhesive coatedparting film and a new piece of pre-preg was used and the processrepeated. Up to 15 cycles (with a single coupon of adhesive coatedparting film) were performed.

To determine the amount of resin transfer, FTIR spectroscopy was used tomeasure the resin surface concentration after 1× and 15× pre-pregcontact cycles for CALPRENE 540 and SOLPRENE 9618 adhesives on Coronatreated PET parting film. Selected results for the CALPRENE adhesive areshown in FIG. 5. After 15× pre-preg contact cycles, the IR showsessentially no peak for the pre-preg resin. Although lacking a peak, theIR intensity is increased relative to the Caplrene 540 adhesive control.The origin of this increased intensity is not fully understood but mayoriginate from surface roughness changes due to contact with thepre-preg. Despite seeing no clear peak from the resin, simply using theIR intensity near 3365 cm⁻¹ gives a surface concentration of <1.1μg-resin/cm², which is close to our estimated detection limit for the IRmeasurement. The results for 15× cycles with SOLPRENE 9618 are shown inFIG. 6. For this test, a clear peak from the resin is seen, although itis slightly shifted from the peak in the CALPRENE standard. The cause ofthis shift is not understood. Nevertheless, using the peak intensitygives a surface concentration of <1.0 μg-resin/cm².

Additional details regarding the resin transfer quantification methodwill now be discussed. Use of IR spectroscopy to quantify resin build-upon the adhesive requires at least moderately strong adsorption bandsfrom the resin that do not significantly overlap with bands from theadhesive. FTIR spectra of the as-received CALPRENE 540 adhesive and apiece of pre-preg (pressed with force against the ATR plate) are shownin FIG. 7. The spectrum of the pre-preg has several bands from the resinthat do not overlap with bands from the adhesive. For the band at 3365cm⁻¹, there are no nearby bands from the adhesive and the intensity inthat region is featureless (FIG. 7, left inset). Two other bands withoutsignificant overlap occur at 1145 cm⁻¹ and 1510 cm⁻¹ (FIG. 7, rightinset). The band at 3365 cm⁻¹ is only about 20% as strong as the bandsat 1145 cm⁻¹ and 1510 cm⁻¹. However, these bands are not as favorable asthe band at 3365 cm⁻¹ because there is a weak band from the adhesivenear 1145 cm⁻¹ and a relatively strong band near 1510 cm⁻¹. For theanalysis method described herein, the band at 3365 cm⁻¹ was used.

As seen, for example, in FIG. 7 and in detail in FIG. 8, the baselinesfor different spectra can differ by up to ˜0.01 absorbance units. Whilesmall, this difference is unacceptable for accurate quantification ofsmall amounts of resin build-up on the adhesive surface. To account forthis difference, a two point linear background was subtracted from thespectra. The preferred locations of the background points at ˜3800 cm⁻¹and ˜2200 cm⁻¹ are shown in FIG. 8.

Prior to subtracting the background, the spectra intensity wereconverted from absorbance [I(abs)] into transmission [I(trans)] usingthe standard relationship, I(trans)=10^(−I(abs)), so that intensitychanges could be linearly related to concentration. An example, of aspectrum containing resin deposited on the adhesive (as described below)in transmission together with and linear background is shown in FIG. 9.A linear background was found to fit the spectra well over the region2000 cm⁻¹ to 4000 cm⁻¹, which contains the preferred band forquantifying the resin (3365 cm⁻¹) and C—H stretch bands from theadhesive (major band at 2916 cm⁻¹).

To obtain a background corrected spectrum in transmission but displayedwith a zero (as opposed to a unity or 100%) baseline designated as((trans, background corrected, zero baseline), the spectra wassubtracted from the background [I(background)] using I(trans, backgroundcorrected, zero baseline)=I(background)−I(trans). For example, in FIG.9, the straight line background between the two data points minus thelower spectrum shown in the graph.

Several examples of the resulting spectra are shown in FIG. 10. Withthis conversion to transmission and background correction, the baselinesfor most spectra taken, e.g., FIG. 10, are nearly indistinguishable.Importantly, the band at 3365 cm⁻¹ from resin build-up is clearly seenwith transmission intensity spanning at least a factor of 20 relative toa common baseline. This enables the amount of resin on the adhesive tobe quantified, as described below. Ideally, these transformations wouldalso yield indistinguishable peak intensities for the adhesive. However,as shown in the inset to FIG. 10, the peak intensity for the main C—Hstretch at 2916 cm⁻¹ varies by 10%, from 0.20 to 0.22. Thus, anadditional multiplicative normalization could be applied to the spectra.This was not done because the variability is relatively small, only˜10%.

Using spectra such as those shown in FIG. 10, resin build-up on theadhesive may be quantified by determining a calibration curve for thepeak intensity at 3365 cm⁻¹, (e.g., intensity versus resinconcentration). This calibration curve is determined by measuringspectra for a set of resin-on-adhesive calibration samples, which haveindependently known resin concentrations. To fabricate calibrationsamples, standard solutions of resin dissolved in acetone were preparedas follows.

A stock solution of pre-preg resin dissolved in acetone was prepared bysonicating a 0.7 g sample of pre-preg in 30 g of acetone in a sealedvial for ˜5 min. Immediately after sonication the acetone solution wasstill cloudy. The sample was allowed to sit for ˜3 days during whichtime the solution cleared. The solution was then poured off from theremaining pre-preg to fix the resin concentration. The resinconcentration was determined by evaporating 5.2516 g of solution in a60° C. oven. A residual weight due to the resin of 0.0356 g wasobtained. Thus, the stock solution had a concentration of 0.0068g-resin/g-solution.

To deposit resin onto the adhesive several procedures were evaluated.The two most important and related criteria for evaluating theprocedures are 1) spatially uniformity over the ATR plate area and 2)reproducible intensity of the resin band at 3365 cm⁻¹ for nominallyidentical resin concentration samples.

The procedure selected used diluted resin/acetone solutions deposited asmany small droplets onto heated samples of the adhesive. A 10 μlcapillary pipette was used with small drops dabbed over a chosen area byrepeatedly lightly touching the end of the capillary to the adhesive.The pipette was used without a plunger and was filled by capillaryaction. Each “dab” was roughly estimated to deposit <˜0.5 μl, ˜20droplets for 10 μl of the resin solution. Each drop spread over only asmall portion of the area, so the overall uniformity was achieved bydistributing these droplets over the ATR area by hand. In addition, theadhesive substrates were heated by being laid on a hot plate set at 70°C. In contrast, if a full 10 μl drop was deposited in a single stepusing the pipette with the plunger, evaporation of the drop was notuniform. As the drop evaporated, it would break up into smaller dropswith the result that the deposited resin (which could be discernedoptically) ended up in small concentrated spots, often near the edges ofthe initial drop. Using many small droplets mitigated this problem,although uniformity remained an issue. The measured IR intensities stillhad considerable scatter but averaging ˜5 samples for each resinconcentration appeared to give consistent results.

From the stock pre-preg resin/acetone solution, made with a resinconcentration of 0.0068 g-resin/g-solution, dilutions of 1:10 to 1:500,were prepared. Using these solutions, standard resin-on-adhesive sampleswere prepared by dabbing 10 μl of solution onto the adhesive over a 0.75cm diameter circular spot, an area of 0.44 cm². These standard sampleswere used to obtain the calibration curve shown in FIG. 11 from the peakintensity of the (1−Transmission) background corrected IR spectra at3365 cm⁻¹. The top axis shows the diluted resin solution concentrations,which can be used as a guide for future calibrations. The bottom axisshows the resin surface concentration, determined from the resinsolution concentration, the solution density (assumed to be the densityof acetone, 0.791 g/cm³), the total volume deposited (10 μl=0.01 cm³)and the area (0.44 cm²). For example, for a 1:50 dilution: 0.0068g-resin/g-acetone·1/50·0.791 g-acetone/cm³·0.01 cm³/0.44 cm²=2.4μg-resin/cm². The behavior appears linear although there is scatter fromthe nonuniformity of the standard samples. The line shown is a fit forthe samples with resin surface concentrations from 1.2 μg/cm² to 12μg/cm².

From the linear fit shown in FIG. 11, the resin surface concentrationfor an unknown sample may be determined by inverting the fit. Thisinversion (surface resin concentration as a function of IR intensity at3365 cm⁻¹) is shown in FIG. 12 together with upper and lower limitsdetermined from the ±1σ variation of the linear fitting parameters, theslope and intercept. For this calibration: Resin concentration(g/cm²)=[(Intensity at 3365 cm⁻¹)−0.00164]/1345. The lower limit is:Resin concentration (g/cm²)=[(Intensity at 3365 cm⁻¹)−0.00232]/1445. Theupper limit is: Resin concentration (g/cm²)=[(Intensity at 3365cm⁻¹)−0.00095]/1245. We note that this calibration strictly applies onlyto the FTIR system used for these experiments and should be used withcaution on other systems. Ideally, for each system used, a set ofstandard samples should be measured as shown in FIG. 11.

From the low concentration samples (FIG. 11, dilutions of 1:200, 1:300,and 1:500) a detection limit for the pre-preg resin on the adhesivemeasured by IR was estimated. FIG. 13 shows background corrected1-Transmission spectra for two 1:200 dilution standard samples(nominally 0.6 μg/cm²) shown as dotted lines, and one 1:500 dilutionsample (nominally 0.24 μg/cm²) shown as dashed lines. These spectra wereacquired with 1024 scans. No peak is observed for the 1:500 dilutionsample. Similarly no peaks were observed for 1:300 dilution samples (notshown). For the 1:200 samples, one spectrum shows a clear peak while theother shows just the beginnings of a peak rising above the background.From these data and the fits shown in FIG. 11, we estimate the detectionlimit for this measurement to be about 1 μg-resin/cm²-adhesive.

Notwithstanding that the numerical ranges and parameters setting forththe broad scope of the disclosure are approximations, the numericalvalues set forth in the specific examples are reported as precisely aspossible. Any numerical value, however, inherently contains certainerrors necessarily resulting from the standard deviation found in theirrespective testing measurements. Moreover, all ranges disclosed hereinare to be understood to encompass any and all sub-ranges subsumedtherein.

While the present teachings have been illustrated with respect to one ormore implementations, alterations and/or modifications can be made tothe illustrated examples without departing from the spirit and scope ofthe appended claims. In addition, while a particular feature of thepresent teachings may have been disclosed with respect to only one ofseveral implementations, such feature may be combined with one or moreother features of the other implementations as may be desired andadvantageous for any given or particular function. Furthermore, to theextent that the terms “including,” “includes,” “having,” “has,” “with,”or variants thereof are used in either the detailed description and theclaims, such terms are intended to be inclusive in a manner similar tothe term “comprising.” Further, in the discussion and claims herein, theterm “about” indicates that the value listed may be somewhat altered, aslong as the alteration does not result in nonconformance of the processor structure to the intended purpose described herein. Finally,“exemplary” indicates the description is used as an example, rather thanimplying that it is an ideal.

It will be appreciated that variants of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be combined intomany other different systems or applications. Various presentlyunforeseen or unanticipated alternatives, modifications, variations, orimprovements therein may be subsequently made by those skilled in theart which are also intended to be encompasses by the following claims.

What is claimed is:
 1. A method of making a plurality of compositeparts, the method comprising: covering a mold tool for a composite partwith a parting film, the parting film comprising a polymer sheet and apressure sensitive adhesive, the parting film being positioned so thatthe polymer sheet is between the mold tool and the pressure sensitiveadhesive; forming a first composite part by carrying out (i) a laying upprocess comprising laying up at least one layer of pre-preg on theparting film covering the mold tool to form the first composite part,the pre-preg comprising an adhesive; and (ii) removing the firstcomposite part from the parting film; and repeating (i) and (ii) to forman additional composite part, the first composite part and theadditional composite part being formed without removing the parting filmfrom the mold tool.
 2. The method of claim 1, wherein the laying upprocess and the removing are carried out 5 to 50 times without removingthe parting film from the mold tool.
 3. The method of claim 1, whereinthe pressure sensitive adhesive adheres to the at least one layer ofpre-preg while laying up occurs, the pressure sensitive adhesivereleasing the first composite part during the removing of the firstcomposite part from the mold tool.
 4. The method of claim 1, wherein thepolymer sheet comprises a material chosen from polymers of polyethylene,polyethylene terephthalate (“PET”), fluorinated ethylene propylene(“FEP”), nylon and combinations thereof.
 5. The method of claim 1,wherein the polymer sheet is a Corona-treated polymer sheet to improveadhesion.
 6. The method of claim 1, wherein the pressure sensitiveadhesive has an elasticity ranging from 50% to 1000%.
 7. The method ofclaim 1, wherein the pressure sensitive adhesive comprises a materialchosen from adhesives of acrylic resin, polyurethane, rubber,styrene-butadiene-styrene copolymer, ethylene vinyl acetate, styreneblock copolymers and combinations thereof.
 8. The method of claim 1,wherein the pressure sensitive adhesive comprises a material chosen fromadhesives of styrene-butadiene-styrene block copolymers,styrene-butadiene-styrene random copolymers and combinations thereof. 9.The method of claim 1, wherein the pressure sensitive adhesive has amass average molecular weight of about 70,000 g/mol to about 1,500,000g/mol.
 10. The method of claim 1, wherein the pressure sensitiveadhesive comprises a block copolymer having a first block and a secondblock, the first block having a glass transition temperature of lessthan 20° C. and the second block having a glass transition temperatureof greater than 20° C.
 11. The method of claim 1, wherein removing thefirst composite part is performed with a tool that adheres to thepre-preg more strongly than the pressure sensitive adhesive of theparting film.
 12. The method of claim 11, wherein the tool is a vacuumchuck.
 13. The method of claim 11, wherein the tool comprises anadhesive that adheres to the pre-preg.
 14. The method of claim 1,wherein a surface of the first composite part contacts the parting filmduring laying up of the pre-preg, and less than 10 micrograms/cm² of thepressure sensitive adhesive remain on the surface of the first compositepart after removing the first composite part from the parting film. 15.A method of making a plurality of composite parts, the methodcomprising: covering a mold tool for a composite part with a partingfilm, the parting film comprising a polymer sheet and a pressuresensitive adhesive, the parting film being positioned so that thepolymer sheet is between the mold tool and the pressure sensitiveadhesive; forming a first composite part by carrying out (i) a laying upprocess comprising laying up at least one layer of pre-preg on theparting film covering the mold tool to form the first composite part,the pre-preg comprising an adhesive; and (ii) removing the firstcomposite part from the parting film; and repeating (i) and (ii) to forman additional composite part, the first composite part and theadditional composite part being formed without removing the parting filmfrom the mold tool, wherein the pressure sensitive adhesive comprises amaterial chosen from adhesives of acrylic resin, polyurethane, rubber,styrene-butadiene-styrene copolymer, ethylene vinyl acetate, styreneblock copolymers, and combinations thereof.
 16. The method of claim 15,wherein the polymer sheet comprises a material chosen from polymers ofpolyethylene, polyethylene terephthalate (“PET”), fluorinated ethylenepropylene (“FEP”), nylon and combinations thereof.
 17. The method ofclaim 15, wherein the polymer sheet is a Corona-treated polymer sheet toimprove adhesion.
 18. The method of claim 15, wherein the pressuresensitive adhesive has an elasticity ranging from 50% to 1000%.
 19. Themethod of claim 15, wherein the pressure sensitive adhesive comprises amaterial chosen from adhesives of styrene-butadiene-styrene blockcopolymers, styrene-butadiene-styrene random copolymers and combinationsthereof.
 20. The method of claim 15, wherein the pressure sensitiveadhesive has a mass average molecular weight of about 70,000 g/mol toabout 1,500,000 g/mol.
 21. The method of claim 15, wherein the pressuresensitive adhesive comprises a block copolymer having a first block anda second block, the first block having a glass transition temperature ofless than 20° C. and the second block having a glass transitiontemperature of greater than 20° C.